1. Technical Field
The present invention relates to a driving device, a projector, and a driving method.
2. Related Art
In a projector or the like, a location of a lens is controlled by a driving device.
A driving system of a lens structurally has backlash, and when driving the lens in a reverse direction with respect to a last moving direction, it is difficult to move the lens to a proper location due to influence of the backlash.
In an example of a general configuration, a location sensor is provided near a motor, the location is detected by the location sensor in advance, a driving target (herein, lens) exists on a rear stage thereof, and accordingly, if the motor starts moving, the location sensor reacts in advance, and then, the driving target starts moving. Thus, the backlash can be compensated based on the detection results of the location by the location sensor.
In detail, as an example, by moving the driving system for an amount of the backlash, using information of the backlash amount acquired by previous measurement or the like, by monitoring output (detection results of the location) from the location sensor, the backlash can be compensated (for example, see Japanese Patent No. 3208802). As another example, by filling the backlash part by setting the motor to have low torque, the backlash can be compensated (for example, see JP-A-10-160999). In addition, as an example of a method of measuring the backlash amount, the location is detected while driving the motor at low torque, the backlash amount can be measured based at a time point when a moving rate is changed (for example, see JP-A-2007-187712).
However, when aiming to achieve miniaturization of the device, the location sensor is not always provided near the motor as the configuration described above.
For example, a driving target (herein, lens) is immediately moved by a motor and many gears exist from the motor to the location sensor, and a case of using a configuration that backlash becomes large from the motor to the location sensor is considered. In this case, since a driving target starts moving before the location sensor detects the location, it is difficult for the location sensor to detect the movement of driving target, and a movement amount acquired from the location sensor becomes smaller than the actual movement amount.
Accordingly, for example, a method of moving extra backlash part (for example, see Japanese Patent No. 3208802) is difficult to be used since the movement detected by the location sensor is smaller than the movement of the driving target. In addition, a method of filling the backlash part (for example, see JP-A-10-160999) is difficult to be used since the driving target is moved before the backlash related to the location sensor is filled. A method of measuring the backlash amount at low torque driving (for example, see JP-A-2007-187712) is difficult to be used since the change of the moving rate does not occur due to the movement of the driving target before the movement of the location sensor.
As described above, on the other hand, with respect to the configuration of the related art of providing the location sensor nearer to the motor than the driving target, in a configuration of providing the driving target nearer to the motor than the location sensor, a location relationship between the driving target and the location sensor is reversed, and the methods related to the backlash which were effective in the configuration of the related art (for example, see Japanese Patent No. 3208802, JP-A-10-160999, and JP-A-2007-187712) are difficult to be used.
As described above, in the related art, in the driving device of the configuration of providing the driving target nearer to the motor than the location sensor, there was a problem that control related to the backlash was not sufficient.